import java.util.Comparator;
import java.util.Set;
import java.util.TreeSet;

class Student implements Comparable<Student>{
    private String name;
    private int age;

    @Override
    public int compareTo(Student o) {
        return this.age-o.age;
    }

    public Student(String name, int age) {
        this.name = name;
        this.age = age;
    }

    @Override
    public String toString() {
        return "Student{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }
}
public class Test {
    public static void main(String[] args) {
        Set<Student> students=new TreeSet<>(new Comparator<Student>() {
            @Override
            public int compare(Student o1, Student o2) {
                return Integer.compare(o1.getAge(),o2.getAge());
            }
        });
        Student stu1=new Student("张三",25);
        Student stu3=new Student("李四",21);
        Student stu2=new Student("王五",21);
        Student stu4=new Student("老六",23);
        students.add(stu1);
        students.add(stu2);
        students.add(stu3);
        students.add(stu4);
        System.out.println(students);

    }
}
